Field of the Invention
The invention relates to a target and an X-ray tube, and particularly relates to a composite target and an X-ray tube with the composite target.
Description of Related Art
An X-ray tube can be broadly divided into a transmission type X-ray tube and a reflection type X-ray tube, which is suitable for medical image, industrial testing, and other technical fields.
FIG. 1 is a schematic diagram of a conventional transmission type X-ray tube. Referring to FIG. 1, a transmission type X-ray tube 100 includes a cathode 110, a focusing mechanism 120, an end window anode 130, a target 140, a power source supply 150, and a vacuum casing 160. An electron from the cathode 110 is accelerated along an electron beam path 170, so as to hit the target 140 to generate an X-ray 180.
Referring to FIG. 1, the focusing mechanism 120 is used to focus on the electron, so as to control the position where the electron hits the target 140. The power source supply 150 is connected between the cathode 110 and the end window anode 130 to provide the energy for the electron, so as to accelerate the electron. The generated X-ray 180 penetrates through the end window anode 130 and emits to the outside of the vacuum casing 160.
FIG. 2 is a schematic diagram of a conventional reflection type X-ray tube. Referring to FIG. 2, a reflection type X-ray tube 200 includes a cathode 210, an anode 220, a power source supply 230, a side window 240, and a vacuum casing 250. An electron from the cathode 210 is accelerated along an electron beam path 260, so as to hit the target (not shown) contained on the anode 220, thereby generating an X-ray 270 at the anode 220.
Referring to FIG. 2, the power source supply 230 is connected between the cathode 210 and the anode 220 to provide the energy for the electron, so as to accelerate the electron. The generated X-ray 270 is reflected toward the side window 240 at the anode 220, and then emits to the outside of the vacuum casing 250.
The transmission type X-ray tube 100 using the conventional single target as shown in FIG. 1 has the following issues which are illustrated by FIG. 3.
FIG. 3 illustrates an output spectrum of a transmission type X-ray tube. In FIG. 3, a fixed tube voltage of 120 kV is used. It shows the relationship between the energy band of the X-ray photon on the horizontal axis and the amount of the X-ray photon on the vertical axis under the condition that tantalum with different thickness (13 μm, 50 μm, and 100 μm) is used as the target.
Referring to FIG. 3, it can be learned that each target with different thickness (13 μm, 50 μm, and 100 μm) has different bremsstrahlung distribution. When it is desired to use different bremsstrahlung distribution, it is required to correspondingly replace the target with different thickness, so that the use is quite inconvenient.
The amount of the X-ray photon of the conventional transmission type X-ray tube can be adjusted by using the methods such as adjusting the thickness, tube voltage, and tube current of the target. However, it is still difficult to obtain the required X-ray energy spectrum distribution.
The reflection type X-ray tube 200 as shown in FIG. 2 has the following issues which are illustrated by FIG. 4. FIG. 4 is a diagram illustrating the comparison between an output spectrum of a transmission type X-ray tube and an output spectrum of a reflection type X-ray tube. The transmission type X-ray tube uses tantalum with a thickness of 25 μm as the target, and a filter layer is not provided; and the reflection type X-ray tube uses tungsten (W)+aluminum (Al) (1.6 mm) as the target. In FIG. 4, the horizontal axis represents the energy band of the X-ray photon, and the vertical axis represents the amount of the X-ray photon. Also, FIG. 4 shows the distribution of the X-ray photon of the two when the tube voltage is set at 120 kV.
Referring to FIG. 4, at the same tube voltage (120 kV), the amount of the high energy photon of the X-ray of the reflection type X-ray tube is far more than the amount of the high energy photon of the X-ray of the transmission type X-ray tube. For the reflection type X-ray tube, the energy spectrum distribution ratio can be changed by increasing the tube voltage. Corresponding to the object with different thickness, the number of the X-ray photon which can penetrate the object to be tested can be increased by changing the tube voltage, so as to improve the image contrast ratio.
However, as shown in FIG. 4, the amount of the low energy photon of the X-ray of the reflection type X-ray tube is usually too much, which causes unnecessary radiation absorbed dose for human body.
Additionally, if the target is bombarded by the electron for a long time, the loss of the surface material of the target is generated. Also, since the target is hit by the electron, it becomes a high-temperature target, and the temperature which is close to the melting temperature of the target is often achieved. Thus, the target is subjected to high evaporation rate at the melting temperature, so as to shorten the life of the target.